Easeful,
I would call either social services for seniors or a doctor and see what they advise. You could try calling one of them over the weekend if she is really getting worse. I am sure there are 800 numbers you could call. You might try calling the er and explaining to them what you told us and ask them what you could do. You are so right she needs help and she needs it now.
You are right if you just let her be and let her die it is the easy way out but you will have guilt later.
Hugs and prayers coming to you